This invention relates generally to CMOS Driver Circuits, and more particularly to CMOS Driver Circuits which include a feedback arrangement which allows the driver circuit to drive transmission line networks and especially off-chip transmission line networks which may vary widely in their total capacitance and drive such loads rapidly even when there is a relatively large total capacitance, and without "ringing" or "reflections" when the total capacitance is relatively small.
There are many driver circuits which are designed to drive mainly capacitance loads, in particular off-chip capacitance devices, wherein the driver circuit must be able to handle a multiplicity of such devices having a wide range of total capacitance depending on what devices are being utilized in combination with the driver circuit. These particular driver circuits are typically designed in submicron CMOS Technology and a given driver circuit may be matched with any one of a number of different capacitance devices or arrays of such devices depending on the design and the end result desired. For example, a given driver circuit may be required to drive such devices which may have total capacitance ranging from as little as 10 picofarads ("pf's") to as much as 100 pf's, the same CMOS driver being required to handle this entire range of total capacitance of off-chip devices. If the CMOS driver circuit is designed to operate extremely rapidly in order to handle the 100 pf capacitance of the devices and it were attached to devices having a total capacitance of only 10 pf, a very rapid charging, or slew rate, (normally measured in volts per nanosecond), can result in a condition known as "reflections" or "ringing" which means the signal is difficult or impossible to detect, or alternatively a long time is required for the signal to stabilize so that it can be read. If on the other hand, the circuit is designed so as to avoid "ringing" when driving devices having total capacitance as low as 10 picofarads, then if it is connected to capacitance devices of 100 picofarads, the slew rate is so slow that it takes a long time to fully charge the devices which results in loss of the efficiency of the driver circuit.
It is therefore desirable to provide a circuit which will operate sufficiently rapidly when charging capacitance devices having a high total capacitance but still operate without "ringing" or "reflections" when charging devices having a relatively low total capacitance, and it is the principal object of the present invention to provide a CMOS driver circuit which operates in such a manner.